This application relates to drill bit fabrication.
Various industrial elements (e.g., drill bit cutters) may include one or more polycrystalline diamond compact (PDC). A PDC may, for example, provide very high thermal and abrasion resistance to a fixed cutter or other industrial element, along with other possible benefits. The PDC portion of the element may be formed by subjecting small diamond particles to high temperature and pressure. The PDC may be formed directly on the surface of a substrate, which typically forms the main body of the element. A catalyst (e.g., Fe, Ni, Co, and alloys thereof) may be included with the loose diamond particles and/or may be present in the substrate to migrate out of the substrate at elevated temperature and pressure. Subjecting the diamond particles and substrate to extreme temperature and pressure causes the diamonds to fuse together and form a generally continuous and physically solid matrix, which constitutes the PDC. In this matrix, there are substantial direct diamond-to-diamond bonds. After formation, the catalyst materials remain interspersed in the interstitial spaces of the PDC matrix. As a result of the forming process, the PDC is also bonded to the substrate in such a way that the PDC stays in place on the substrate when the element is in use.
During industrial use of the element, such as when drilling with a fixed cutter drill bit, any catalyst in the interstitial spaces of the PDC may confer detrimental properties to the PDC over time. For example, the catalyst may have a higher coefficient of thermal expansion than diamonds such that, as the PDC element heats up during use, the metal catalyst may expand faster than the diamond matrix. This disproportionate expansion may cause problems such as spalling, delamination, or conversion to graphite, which may limit the lifetime of the PDC.
To increase the mechanical properties and useful lifetime of PDC, some catalyst may be removed from at least a working surface of the PDC. Removal of the catalyst is typically accomplished using either an electrochemical or a chemical process. In chemical processes, commonly referred to as “leaching,” the PDC may be soaked in a strong acid or a caustic material to dissolve and remove the catalyst from the interstitial spaces of the PDC. Depending on the desired leaching depth, the soaking processes may take several days to weeks. In some instances, the leaching process may be over a month.